1. Field of the Invention
The present invention relates to electronic musical instruments, and more particularly, to electronic musical instruments capable of simulating the sound of conventional non-electronic musical instruments with high fidelity.
2. Prior Art
Due to recent technological improvements, tone generating devices employed in electronic musical instruments have become available which are capable of synthesizing a wide variety of musical tones. For example, tone generating devices are conventionally known which synthesize tones which effectively simulate the sound of a conventional non-electronic musical instrument by simulating the mechanism of sound production in the target non-electronic instrument.
One example of such a conventional tone generating device suitable for simulating the sound generating mechanism of conventional stringed instruments is shown in the block diagram of FIG. 8. In this figure, an excitation signal generating circuit 1a can be seen which includes waveform memory wherein excitation signal waveforms such as impulse waveforms are stored which are made up of a large number of different high frequency components. Additionally, the illustrated device includes a closed loop circuit consisting of an adder 2, delay circuit 3 and filter 4.
Excitation signals output from excitation signal generating circuit 1a are supplied to the closed loop circuit via an input terminal of adder 2. The output signal from adder 2 is supplied to delay circuit 3 which simulates the delay of propagation of vibrating waves in a string of the target stringed instrument. The delayed output signal of delay circuit 3 is then supplied to filter 4 which simulates acoustical losses of a vibrating string of the target instrument. The output signal of the filter 4 is then supplied to a second input terminal of adder 2, in this way forming a closed loop. In addition to delay circuit 3, the output signal of adder 2 is supplied to a sound signal output terminal 5, whereby a musical tone signal circulating in the closed loop can be sampled to generate an output signal.
With the conventional tone generating device described above, after an excitation signal from excitation signal generating circuit 1a is supplied to adder 2, the excitation signal thus input into the closed loop begins to circulate thereabout, such that the time required for the signal to travel around the closed loop one time is equal to the period of oscillation of the vibrating string being simulated. An example of the above described type of tone generating device has been disclosed in Japanese Patent Application Second Publication, Serial No. Sho-58-48109.
An example of a conventional tone generating device suitable for simulating the sound generating mechanism of woodwind instruments is shown in the block diagram of FIG. 9, wherein an excitation signal generating circuit 1b can be seen similar to the excitation signal generating circuit 1a described above. In the case of the device shown in FIG. 9, the output signal of the excitation signal generating circuit 1b is supplied to a loop circuit via a subtracter 7 and an adder 8, both of which are components of the loop circuit. As FIG. 9 shows, immediately between subtracter 7 and adder 8, a nonlinear element 6 is included as a component of the loop circuit which simulates the nonlinear characteristics of a reed which is the sound generating element in the woodwind instrument under simulation. Subtracter 7 and adder 8 on either side of nonlinear element 6 simulate the application of air pressure to the reed in the instrument being simulated.
Delay circuits 9 through 12 can be seen, each consisting of, for example, multiple stage shift registers. These delay circuits 9 through 12 simulate the delay of transmission of air pressure waves in tubular portions of the simulated wind instrument. Delay circuits 9 and 10 correspond to tubular portions of the instrument tubes nearest to the reed, while delay circuits 11 and 12 correspond to those farthest from the reed. Delay circuit 9 receives the output signal from adder 8, whereas delay circuit 10 supplies an input signal to subtracter 7 wherein the output of delay circuit 10 is subtracted from the output signal from excitation signal generating circuit 1b.
A junction circuit 13 is incorporated into the loop circuit which simulates the scattering of air pressure waves caused by variations in the diameter of tubular portions of the woodwind instrument being simulated. In this junction circuit 13, a fourth order multiplier lattice is used which consists of multipliers 14.sub.1 -14.sub.4 having multiplication coefficients K.sub.1 -K.sub.4, respectively, controlled by a control circuit (not shown), and which correspond to wave scattering characteristics of tubular portions of differing diameters. Junction circuit 13 additionally includes an adder 15.sub.1 which adds the output of multiplier 14.sub.1 to the output of multiplier 14.sub.4, and an adder 15.sub.2 which adds the output of multiplier 14.sub.2 to the output of multiplier 14.sub.3. The output signal from the above mentioned delay circuit 9 is transmitted to the delay circuit 11 via multiplier 14.sub.1 and the output signal from above mentioned delay circuit 12 is transmitted to delay circuit 10 via multiplier 14.sub.2.
A filter 16 is provided in the loop circuit of the tone generating device shown in FIG. 9 which simulates acoustical losses in the tubular portions of the simulated woodwind instrument reflecting the physical configuration thereof. A multiplier 17 intervenes between filter 16 and delay circuit 12 which serves to simulate such factors as dissipation of acoustical energy which takes place when pressure waves are reflected from the terminal portions of the woodwind instrument. The multiplication coefficient g1 of multiplier 17 is controlled by the previously mentioned control circuit, and the output signal from delay circuit 11 is multiplied thereby, the result of which is then supplied to delay circuit 12. An example of the type of tone generating device thus described has been disclosed in Japanese Patent Application First Publication, Ser. No. Sho-63-40199.
As was described above, filter 4 employed in the conventional tone generating device shown in FIG. 8 and filter 16 employed in that shown in FIG. 9 act to simulate the acoustical losses which occur in a vibrating string of a simulated string instrument, and acoustical losses affecting pressure waves in the tubular portions of a simulated woodwind instrument, respectively. Because such acoustical losses have time varying characteristics, filters which simulate such losses tend to be quite complex. This is especially problematic when simulating losses having a complicated envelope describing time dependent filter characteristics, such that the necessary filter circuits must often be of third order and higher, with exceedingly complex structures and design requirements. As a consequence, unless such highly complex and therefore expensive filters are made use of, the sound of the target non-electronic instruments can be simulated with only limited fidelity, such that the achieved effect tends to sound unnatural.
Accordingly, there is a significant demand for tone generating devices to be used in electronic musical instruments which simulate the sound of one or more target non-electronic musical instruments by simulating the mechanism of sound production thereof, which can produce a highly natural sounding musical effect which simulates the sound of the target instruments with exceedingly high fidelity, and furthermore, which do not require the use of highly complex electronic filtering circuits in order to accurately simulate time varying acoustical losses which occur in the target instruments.